Impairment and disability resulting from claims of multiple chemical sensitivity (MCS) challenge independent medical examiners because of polemics associated with the syndrome, and the mainstream medical community has questioned its very existence as a medical disease entity. Since the syndrome was described in 1952, MCS has had many names, including universal allergy, total allergy syndrome, ecologic illness, 20th century disease, and chemical AIDS. Epidemiologic data show that a higher proportion of females (up to 88%) suffer from MCS, and the percentage of unemployment among MCS sufferers may be as high as 85%. The best explanation to date for MCS is that it is an illness belief system manifested by culturally shaped illness behavior. Several distinguished scientific organizations, including the AMA, conclude that there is no scientific evidence to support the MCS concept of a physiologic exposure–disease relationship; the proposed diagnostic tests and treatments have not been shown to have value; and MCS should not be a recognized clinical syndrome. Impairment evaluations should follow the guidelines in Chapters 1 and 2 of the AMA Guides to the Evaluation of Permanent Impairment. Evaluators must recognize that MCS claimants often present with comorbid psychiatric conditions, and iatrogenic disability also is a concern among MCS patients.